This is a prospective overview of new avenues of animal research in sleep physiology in the Clinical Psychobiology Branch. Our experimental aim is to investigate unresolved, basic sleep research issues. During the last four months, we have formulated the issues which we will address as well as the experimental designs. We are currently making good progress in devising all allocating equipment necessary to carry out the experiments. The function(s) of sleep remain unknown, even though sleep as a phenomenon has been well described. The long-term goal of our sleep research is to find out what is accomplished physiologically during sleep that cannot be accomplished during wakefulness or rest. Our working assumption is that the limits to the biological significance of sleep are unknown. Below are three initial strategies we will use to study sleep: 1. To remove sleep and not the resulting impairments. By searching or intermediary processes which underlie consequences of sleep los we may be able to infer a function normally fulfilled by sleep. The aim of Study 1 is to determine which sleep loss symptoms in the rat indicate a physiological system primarily affected by deprivation, and which symptoms are secondary effects. 2. To search for functional relationships between two processes which appear to co-vary, such as alterations in sleep and energy balance. In Study 2, the metabolic rate of rats will be manipulated via the thyroid systems to determine whether sleep amounts is lawfully related to changes in metabolic status. 3. To search for intermediary effects f variables which markedly alter normal sleep parameters. Study 3 will investigate a previous report that sleep time is dramatically increased by lack of two specific, essential fatty acids. In Study 4, we will assess whether the sleep-inducing effects of prostaglandins might be due to changes in core or brain temperature